1. Field of the Invention
This invention pertains to a fail-safe device for use principally in the telecommunications field. More particularly, this invention pertains to a fail-safe device for use in conjunction with a thyristor to provide a connection to an electrical ground in response to a sustained over-voltage condition.
2. Description of the Prior Art
The use of fail-safe devices in the telecommunications field is well known. A common device is shown in U.S. Pat. No. 4,866,563 to Howard et al. dated Sep. 12, 1989. The fail-safe device of U.S. Pat. No. 4,866,563 utilizes a gas discharge tube which, in response to a sustained over-voltage condition, attains an elevated temperature. When the elevated temperature is attained, pellets (items 5 and 6 in the patent) melt causing a spring to be urged into electrical contact with conductive surfaces on the gas discharge tube. This results in connecting the conductive surfaces to ground.
In addition to such gas discharge tube fail-safe devices, the telecommunications industry may utilize solid state overvoltage protection devices. An example of a solid state overvoltage protection device is a thyristor which attains an elevated temperature in response to a sustained over-voltage condition. A thyristor utilized in a fail-safe device is shown in commonly assigned co-pending U.S. patent application Ser. No. 07/811,878, filed Dec. 19, 1991, now U.S. Pat. No. 5,155,650.
It is an object of the present invention to provide a fail-safe device for use with a thyristor with improved responsiveness and grounding following a sustained over-voltage condition.